The operation of a rotating electric machine, such as a synchronous and induction motor, is based on a magnetic field moving in a stator and rotor. This magnetic field is produced as a joint effect of stator and rotor magnetizations. The currents flowing in the stator windings produce in the air gap of the machine a rotating magnetic field, whose phase difference relative to the rotor magnetization creates a force effect in the direction of motion of the rotor. This force effect causes the rotor to rotate.
The rotor and stator magnetizations together also produce a force of attraction between stator and rotor. The attractive force is usually multiple times greater than the force causing the rotor to rotate. Since the attractive force appears in the zone where the magnetic field is transferred from rotor to stator and vice versa, the attraction vector rotates in accordance with the magnetic field. Therefore, local variations in the attractive force between stator and rotor may produce vibration in the electric machine.
Vibration of an electric machine often produces disturbing noise radiating into the environment, and, on the other hand, it may also shorten the service life of mechanical components of the electric machine. Vibration may also be transferred by transmission e.g. via the mounting interface to the environment, such as to the supporting structures surrounding the electric machine.
It is a general aim to utilize built space as efficiently as possible, for example, owing to space requirements. In the last decade, also the applicant has participated in the development of more compact hoisting machines of elevators. A compact hoisting machine of the applicant, and guide rail fixing arrangment for the same are disclosed in international patent application published under publication number WO 2011/154614 A1. Another compact elevator hoisting machine of the applicant has been disclosed in international patent application published under publication number WO 2011/036348 A1. Both hoisting machines comprise an axial flux motor.
Axial flux motors for hoisting machines are currently being designed to be as flat as possible in their dimensions in the direction of the axis of rotation or as small as possible in their dimensions in the direction of the radius, in which case the hoisting machines fit better in connection with, for instance, the wall part of the elevator hoistway or into some other narrow/shallow space.
However, the rigidity of the hoisting machine may form a problem e.g. when minimizing the length in the direction of the axis of rotation of a hoisting machine implemented with an axial flux motor. For example, rigidity is required of the hoisting machine of an elevator as well as of the support structure of the hoisting machine, because the hoisting machine must support the elevator mechanics suspended in the elevator hoistway. Also the noise level of the hoisting machine may increase to be disturbing when the rigidity of the hoisting machine weakens.
An arrangement for damping vibration in an electric machine, and a corresponding method, have been disclosed in international patent publication published under publication number WO 2010/063869 A1. In the arrangement, vibration dampers are fitted between the stator and the machine frame, or between the stator winding and machine frame.